Keywords
99mTc-MAA - hepatic arterial infusion pump - liver-directed therapy
Introduction
The hepatic arterial infusion pump (HAIP) catheters are surgically inserted in a retrograde
direction into the gastroduodenal artery (GDA) with the tip at the junction of the
GDA and common hepatic artery, allowing arterially delivered chemotherapy via the
pump. In unresectable situations, HAIP is used to deliver chemotherapy agents to cholangiocarcinoma
and colorectal liver metastases. Since the neovascularity of hepatic malignant tumors
is derived predominantly from branches of the hepatic artery, this type of drug delivery
exploits the hepatic first pass metabolism and maximize the drug concentrations in
the tumors alongside decreasing systemic levels of the drug and thereby toxicity.[1]
[2] This approach was previously shown to increase the survival rates of patients.[3]
[4]
Proper functioning of the HAIP system, i.e., the exclusivity of liver distribution
and absence of extra-hepatic perfusion, is ensured by planar and SPECT/CT (single-photon
emission computed tomography/computed tomography) radionuclide imaging with 99mTc-MAA.[5] We bring forth a relatively rare instance when the rate of infusion of the radiopharmaceutical
determines the appearance of the scan.
Case Report
A 35-year-old gentleman with sigmoid colon cancer s/p subtotal colectomy followed
by adjuvant systemic therapy had metastases to liver subsequently. The patient was
next evaluated for a hepatic pump placement for a liver-directed therapy. Pre-therapy
abdominal CT angiography showed that there is trifurcation of right common hepatic
artery, a normal vascular variant ([Fig. 1]).
Fig. 1 Abdominal CT angiography showing trifurcation of right common hepatic artery into
right hepatic artery, left hepatic artery, and gastro-duodenal artery (yellow arrow).
CT, computed tomography.
HAIP was surgically placed over the left anterior abdominal wall with the tip of the
catheter in GDA. Hepatic bilobar methylene blue was seen intraoperatively, confirming
successful pump placement. 5.0 mCi 99mTc-MAA was infused into the pump as a bolus, per usual protocol, to assess the patency
of the pump and evaluate for extra-hepatic abnormal perfusion. As detailed in [Fig. 2], there was heterogenous activity in the right hepatic lobe with minimal activity
within the left hepatic lobe. No extra-hepatic activity noted.
Fig. 2 Planar and SPECT/CT images with 5.0 mCi 99mTc-MAA showing heterogenous activity in the right hepatic lobe with minimal activity
within left hepatic lobe (blue arrow) and no extra-hepatic activity. CT, computed
tomography; SPECT, single-photon emission computed tomography.
Repeat study was done 4 days later with 4.3 mCi of 99mTc-MAA infused at half the usual bolus rate, to simulate real-world chemotherapy infusion
through the port. As detailed in [Fig. 3], the repeat study showed heterogenous bilobar activity and no evidence of extra-hepatic
activity.
Fig. 3 Planar and SPECT/CT images with 4.3 mCi of 99mTc-MAA showing activity in both the hepatic lobes (blue arrow). CT, computed tomography;
SPECT, single-photon emission computed tomography.
Discussion
The HAIP system remains a viable option to control unresectable hepatic metastatic
disease burden and as an adjuvant therapy to decrease recurrence after resected metastases.
When handled as part of a multi-disciplinary team, they are considered safe and efficacious,
with improved patient survival.[6]
HAIPs are manufactured in such a way that the chemotherapy agents are delivered to
the liver from the pump reservoir over a few weeks. The expected findings of a nuclear
medicine liver perfusion scan were previously published.[7] The patient described in the above case report had trifurcation of common hepatic
artery, with right and left hepatic arteries branching from it rather than proper
hepatic artery. It is unclear if this unique appearance on the emission images is
a result of the vascular variance.
This case study highlights the importance of slow infusion of the radiopharmaceutical
during the hepatic pump study, particularly in patients with normal vascular variants.
Appropriate recognition of this pitfall may avoid further unnecessary corrective procedures.
